Secondary batteries such as lithium-ion batteries are installed in hybrid electric vehicles (HEVs) and electric vehicles (EVs). In HEVs and EVs, high voltages are required in order to increase the efficiency of the inverter and the motor. Thus, multiple secondary batteries are connected together. In particular, in lithium-ion batteries, each of the multiple battery cells connected together need to be monitored in order to prevent overcharging and over discharging. A plurality of battery monitoring ICs (integrated circuits) are used in order to monitor the multiple connected battery cells.
Japanese Patent Application Laid-Open Publication No. 2013-104842, for example, discloses a battery monitoring device that includes: a plurality of monitoring means that are provided for each of a plurality of battery modules that constitute a battery assembly, that each monitor the corresponding battery module, and that output monitoring results as an output signal; and a control means that outputs a control signal instructing the plurality of monitoring means to monitor the corresponding battery modules, and that acquires output signals from the plurality of monitoring means. In this battery monitoring device, the plurality of monitoring means are connected in a daisy chain through a first signal line for allowing transmission of the control signal and output signal, and, among the plurality of monitoring means, the high voltage monitoring means corresponding to the battery module on the highest voltage side and the low voltage monitoring means corresponding to the battery module on the lowest voltage side are connected through a second signal line. The control means is connected through an insulated signal transmission means to either the high voltage monitoring means or the low voltage monitoring means, and if there is a break in the first signal line, then the output signal can be acquired through the second signal line.